Cathode-ray tube time base



March 20, 1951 F. E tJ. GIRLING 2,546,065

cATHoDE-RAY TUBE TIME BASE Filed July s1, 1947 4 sheets-sheet 1 March20, 1951 F. E. J. GIRLING 2,546,065

CATHODE-RAY TUBE TIME BASE Filed July 5l, 1947 4 Sheets-Sheet 2 -lov l20w o loo zoo soo 40o ,us

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F. E. J. Girling [nvenlor By 237m Attorney March 20, 1951 F. E. J.GIRLING 2,546,065

cATHoDE-RAY TUBE TIME BASE Filed July 31, 1947 4 sheets-sheet s HOOV-IOOV 0 l0 2O 40 50 60 ,u,S

I F. E. J. G11-lim FIG' 3 Inventar A Harney March 20, 1951 F. E. J.GIRLING 2,546,065

cATHoDE-RAY TUBE TIME BASE Filed July 31, 1947 4 sheets-sheet 4 O IO 2030 40 5D uS `|:'|G 4 F. E. J. Gir-ling Inventor B y J3-...S AttorheyPatented Mar. 20, 1951 CATI-IODE-RAY TUBE TIME BASE Frank Edward J exGirling, Malvern, England Application July 31, 1947, Serial No. 765,199In Great Britain October 23, 1945 Section 1, Public Law 690, August 8,1946 Patent expires April 23, 1965 Claims. (Cl. 315-26) vThis inventionrelates to electronic valve circuits and particularly to circuits usedin pulsed radar sets. Such radar sets produce recurrent pulses of radiofrequency energy, and locking pulses which include a voltage frontcoincident with the transmitted pulse. When following a target eithermanually or automatically the radar set may also produce a voltage pulseor step, usually referred to as a strobe, at a time delay correspondingto the radar echo delay. A presentation unit may be fed with rectifiedsignals, locking pulses and strobes, and may be required to provide adisplay in which the signal being followed, at whatever range it may be,shall appear at the middle of a fast portion of the trace.

The invention therefore comprises a time base circuit adapted to producea recurrent time base voltage sweep initiated in synchronism with arecurrent input voltage front, and arranged to reach a predeterminedvoltage at the time of a recurrent input occurrence having a fixed orslowly-varying time delay relative to said input voltage front, saidmeans comprising an electronic valve circuit which, in the event of saidtime delay varying, tends to reduce any discrepancy between the delayedinput occurrence and the time when the time base voltage reaches thepredetermined voltage. The invention also comprises a cathode ray tubedisplay system including means for producing a slow time base sweep inone direction starting coincident with a recurrent voltage lockingfront, and means for also producing a fast time base voltage sweep ofsubstantially shorter duration in the opposite direction, means forapplying the said voltage sweeps to the opposite deecting plates of acathode ray tube to produce a sweep of the spot on the screen having afast portion, and means for automatically timing the fast sweep so thata repetitive input occurence, which has a xed or slowlyvarying delayfrom the locking front, will always correspond to substantially the sameposition in the fast portion.

Figure l of the accompanying drawings shows a circuit according to theinvention and Figure 2 shows the waveforms appearing at various parts ofthis circuit, the waveforms in Fig. 2 bearing the same reference numbersas the points where they occur bear in Fig. 1. Negative locking pulsesare fed in at I, and in consequence a negativegoing time base sweep isobtained at 3 for application to one deflecting plate of a cathode raytube K. A fast portion is caused to appear in the trace on the screen ofthe C. R. tube by a rapid positive-going time base sweep of shorterduration generated at 9 and applied to the opposite deecting plate. Thestrobe pulse is fed in at 2 and the fast portion is so timed that italways includes the radar strobe.

The operation will now be described in greater detail.

The circuit using the values shown has been found to operate at arecurrence up to 1000 c./s. and the fast portion locks satisfactorily onto a delayed positive strobe of 1 microsecond duration delayed by up toabout 300 microseconds behind the locking pulse.

The symbols n K and M indicate respectively ohms, thousands of ohms, andmegohms. valve types are as shown in the table below. Double diodes anddouble triodes, types VR54 and CVI8I respectively have been freely used.These types include two separate valves in the same envelope, and eachhalf is indicated in the table by 1/ZVRSII and 1/2CVI8I.

VI 1/VR54 VII 12VR54 V2 VRIIS V|2 VZVRSQ V3 lgCVII VI3 VRIIS V4 VRSIVIII 1/2CVI8I V5 1/VR54 VI 5 VRI IB V6 1/VR54 VIG 1/VR54 V'I 1/2VR54 VIT1/2VR54 V8 1/2VR5II VI8 1/2CVI8I V9 VRSI VIS VRQI VID 1/2CVI8 Thenegative front of the negative locking pulse fed to the cathode of diodeVI at I cuts oi the current in the valve V2 by reducing its outercontrol grid voltage. Consequent increase of anode voltage causes thegrid, and therefore the cathode of the valve V3, which were negativelybiassed, to go positive, thus allowing Vthe valve V4 to conduct.`Feedback between the point 3 in the anode circuit of valve V4 and thegrid of this valve by the condenser CI causes this point to falllinearly until it reaches a voltage only slightly positive relative toearth. The anode voltage of valve V4 is communicated by condenser C2 tothe control grid of V2 and cuts off current in this valve, which remainscut off until the sweep has stopped. 'I'he diode V5 prevents the grid ofvalve V5 being driven negative by more than 11 volts, so that when thesweep stops and the grid of V2 starts to recover towards the 300 voltline 4 it only has to recover a few volts before the valve V2 becomeconducting again andthe circuit reverts to its initial condition. Thepoint 3 starts to rise towards the 400 volt line 5 but is stopped at 300volts by the diode V6. The voltage of the The point 6 is determined by acircuit to be described later, and in between sweeps the diode V'I holdsthe point 'l at the same voltage. When the voltage of the point 3 fallsto that of the point 'l the diode V8 starts to conduct, so that thepoint Ti is also carried down positively. This reduces the voltage ofthe point 8 (which was previously held at earth potential by gridcurrent in V9) and cuts oil current in this valve. Current previouslyflowing into this valve is now diverted into the condenser C3 so thatthe voltage o-n the point 9 starts to rise. Thisrise is fed by thecathode follower VI and condenser C4 to the cathode of the diode VII andthe upper end of the resistance RI maintaining a constant voltage acrossRl and therefore a constant rate of change of voltage on the point 9.The sweep continues till it is stopped by the diode VIZ when the pointreaches 300 volts. The sweep on points 3` and 9 with the componentvalues shown, occupy about 300 and l microseconds respectively. Thesetwo points areconnected to the opposite deilecting plates of the cathoderay tube K, and produce a sweep of 300 microsecs. duration with a fastportion lasting 40 microsecs. occurring at a position I determined bythe voltage on the line t. In Figure 2 the voltages on the points 3, 6,l, 8 and 9 shown in Fig. 1 are shown on the same voltage and timescales. As the deilecting plates of the.

Cathode ray tube each cover the range of about 0 to +300 volts the iinalanode is held at the mean 0f these voltage, namely +159 volts. TheStrobe is applied at 2 to the grid of valve Vl5 at a. short and iixed orslowly changing delay after each locking pulse, and the remainingcircuits in Fig. l are provided to ensure that the voltage on the point8 is adjusted to such a value that the fast time base sweep is alwaystimed so that it will have completed about a quarter of its sweep whenthe strobe occurs.

Figure 3 shows further waveform diagrams on a diierent time scale,giving the waveforms which are obtained when the voltage of the point 6is such that the fast time base starts too early, and Fig. 4 shows thewaveforms obtained 'when the fast time base `starts too late.

The fast sweep voltage occurring at the cathode of VID is diierentiatedin the circuit C5, R4 so that the point I0 is brought up to thepotential of the cathode of VI3 and this valve is rendered conducting.At this time the valve VI4 will not be conducting and the point I I,starting from whatever it may happen to be at, will approach a voltagenear to 125 at a rate determined by the product R506. If the valve VIIIremained non-conducting the point II would follow the dotted curve IIain Fig. 3.

The resistances R2 and R3 are so chosen that when the point 9 hascompleted about a quarter of its sweep the point I2 rises to a voltageat which the outer control grid of V permits this valve to pass current.Fig. 3 shows at I2 the voltage on the outer control grid of VIS, which,as the sweep is here assumed to occur too early, reaches cathodepotential at the beginning of the strobe at 2. Further increase in thevoltage of this point is prevented by the diode VIS. During the strobethe valve VI produces a negative pulse at I3. The negatlvegoing leadingedge of this negative pulse is transmitted through the condenser C'i,but point i4 falls by an amount just suiiicient to cause the diode VITto conduct and remains at a potential a little `negative with respect tothe anode of VI?, with diode Vl? just conducting, until the positivegoing trailing edge of the pulse at I3, transmitted through thecondenser Cl, causes point I4 to move positive, thereby cutting 01Tdiode Vil. The resultant positive impulse at I4 causes the valve VI4 toconduct and raises the voltage of the point II to a value determined bythe pulse amplitude aty I3. During the remainder of the time for whichthe valve VI3 is conducting the voltage at I4 decays only slowly andconsequently at the end of the sweep the voltage at i I has only droppedslightly. The valve VIS then becomes non-conducting and the point IIthen remains at substantially the same voltage until the next fast sweepis produced, although by this time the point lli will have returnedsubstantially to the bias of -60 volts. The positive voltage at II isfed by the cathode follower VEB to the integrating valve V i9. The anodeof this valve provides the voltage Ii which in turn determines thetiming of the fast time base sweep. As a result of a positive voltage atIl the point t will fall at a rate proportional to this voltage, and formost rapid correction .the rate of fall of voltage at 6, produced by agiven discrepancy between the timing o f the fast portion and thestrobe, should be such as to remove this discrepancy in the time betweenrecurrences. If the correction is too small the circuit will take anunnecessarily long time to settle down, but if it is too great thecorrection will overfshoot, and in extreme cases the system may becomeunstable. Figure e shows the waveforms corresponding to these in Figure3 which will be produced if the fast time base is too late.` In thiscase the valve Vl will only pass a very small pulse of current andconsequently only a small positive step will be produced at I4, thispoint in fact still remaining negative with respect to earth. The pointII is thus. held only when it reaches a negative voltage, so that thepoint 6 will rise in voltage and so correct the error.

I claim:

l. A cathode ray tube display system comprising a cathode ray tube.means for producing a slow time-base voltage sweep starting coincidentwith a recurrent locking front, means for producing a fast time-basevoltage sweep of substantially shorter duration than said slow timefbase,voltage Sweep and initiated so as to embrace a repetitivefinput pulse,potential regulating means for producing a potential that varies whenthe repetitive input pulses vary their relative time spacings withrespect to Ythe start of their complementary fast timev base sweeps, andmeans responsive to the magnitude of said potential to vary the timespacing between the .Starting in.- stants of therslow and fast sweepsuntil said potential attains av predetermined value and means fordefleeting the electron beam of said cathode ray tube in accordance withthe sum of said two time-base voltages.

2. A cathode ray tube display system comprising a cathode ray tube,means for producing a slow time-base voltage sweep in one direction andinitiated in synchronism with a recurrent input voltage, means forproducing a fast time-base sweep in the opposite direction and ofsubstantially shorter duration than said slow time-base voltage sweep,means for `applying the said voltage sweeps to opposite deecting platesof said cathode ray tube, other deecting plates-for the cathode raytube, means for applying a second repetitive input pulse voltage to saidother plates, means for producing a control voltage which variesaccording to the time diierence between the second input pulse voltagesand the occurrence of a predetermined intermediate voltage of the fasttime base sweep, and means responsive to the magnitude of said controlvoltage for varying the starting time of the fast time base sweep untilsaid control voltage attains a predetermined value.

3. In a time base circuit, in combination, first and second inputcircuits for respectively receiving complementary pulses of spaced pulsepairs; a first sweep generator responsive to the first input forproducing a linearly decreasing sweep potential; a second sweepgenerator including control means which when actuated by a predeterminedypotential starts a sweep of shorter duration than the first-namedsweep; an electron discharge Y device having a cathode, firstV andsecond grids,

and an anode; means connecting the output of the second sweep generatorto said second grid; the electron discharge device being so constructedand arranged as to be non-conducting when the potential of the secondgrid is below a predetermined value; means connecting the second inputto said first grid; means for applying a source of power between theanode and the cathode; a condenser; means for charging said condenserwhen the discharge device passes current; means for producing a controlpotential for controlling the starting time of the next second sweepaccording to the state of charge of said condenser; means applying saidpredetermined potential to the second sweep generator when the potentialof the first sweep generator falls below the said control potential; andmeans for combining the sweep potentials of the two sweep generators.

4. In an indicating system, in combination, a first sweep generatorhaving an input for receiving pulses to initiate sweeps by saidgenerator, a second sweep generator which completes each sweep actionthereof in less than half the time of a complete sweep of the firstgenerator, means for combining the outputs of said sweep generators; andcontrol means to control the time of occurrence of the sweep of thesecond generator and to superimpose its sweep on to that of the firstgenerator, said control means comprising all of the following parts: anelectron discharge device having an anode, a cathode and first andsecond grids, means to control the potential on one of said grids torender the discharge device non-conducting until the Sweep of the second`generator has changed a predetermined amount,

a second pulse input circuit comprising means to apply a positivepotential on the other of said grids when a pulse is received by thesecond pulse input circuit, means for applying a potential across thecathode and anode of said discharge device, and means controlled by thecurrent passing through said discharge device for modifying the timespacing between the start of the sweep of the first generator and thestart of the sweep of the second generator.

5. In an indicating system, in combination, first and second recurrentpulse sources the second of which supplies one pulse for each pulse fromthe first source and spaced in time therefrom, a rst sweep generatorconnected to the first source and having its sweep initiated thereby,said first sweep generator having a sufficiently long sweep time as tocontinue its sweep beyond the time of occurrence of a pulse from thesecond source, a second sweep generator for modifying the sweep of thefirst generator to increase the sweep rate over a predeterminedpercentage of the first-named sweep, and means controlled by the timespacing between complementary pulses from the first and second sourcesto control the time of occurrence of the increased sweep rate .and tocause the latter to overlap the occurrence of pulses from the secondsource.

' 6. The combination of claim 5 including a cathode ray tube havingfirst and second ray deecting elements at right angles to each other,means for impressing the aforesaid sweeps on said first element, andmeans for impressing pulses from the second source on the secondelement.

7. In a time base circuit, in combination, first and second pulse inputcircuits arranged to receive complementary pulses of slowly varying timespacings, a first sweep generator connected to the first input circuitand including means for producing a time base sweep in response to eachpulse received by the rst pulse input circuit, a second sweep generatorfor producing a sweep of less than half the duration of the rst namedsweep, means combining the outputs of said sweep generators, meansresponsive to pulses received in the second pulse input circuit forproducing a control voltage when such pulses occur during predeterminedportions of the second sweep, and means responsive to the potentialoutput of the rst sweep generator for controlling the starting time ofthe next of the recurring second sweeps, the last-named means includingcontrol means for modifying such starting time according to the value ofsaid control voltage.

8. In a time base circuit, in combination, first and second inputcircuits for respectively receiving pairs of complementary pulses withthe pulses of each pair being impressed on said circuits respectively; afirst sweep generator including means for starting its sweep when apulse is received by the first circuit; a second sweep generator whichproduces a sweep of shorter duration than that of the rst sweepgenerator; an electron discharge device having a cathode, first andsecond grids, and an anode; said electron discharge device beingsubstantially non-conducting as long as the potential of the second gridis below a predetermined value; means connecting the output of rthesecond sweep generator between the second grid and cathode, the secondsweep generator including means to give the same such a sweep ofpotential that it reaches said predetermined value at a time spaced fromboth the beginning and end of the sweep; means connecting the secondinput circuit to the first grid; means applying a direct currentpotential between said anode and said cathode; a condenser; means forcharging said condenser according to the flow of current in saiddischarge device; and means responsive to the potential on saidcondenser to increase the time spacing between the sweeps by delayingthe start of the next occurring second sweep when said condenser ischarged.

9. In a sweep generator for producing an expanded sweep portion whichoverlaps the occurrence of pulses which recur at a substantiallyconstant repetition rate and are time spaced from complementary pulses,in combination, a first sweep generator for producing a sweep potentialin response to each of said complementary pulses, a second sweepgenerator which generates one sweep for each sweep of the first-namedgenerator and completes such sweep in less than half the time of thefirst-named sweep, means for combining the outputs of said sweepgenerators, and control means to control the time spacing between thestart of the rst sweep and the start of the second Sweep. said controlmeans compris ing all of the following partis: discharge means havingfirst and second grids for .controlling the same, means for h iallg the`first. grid to cut-off during a `predetermined portion of thesecondnamed sweep, `means for rendering the second grid positive inresponse to each mst-named pulse, and means responsive to the output ofthe discharge device for controlling the second sweep generator to Varythe starting time of the .sweep thereof in accordance with the output ofthe discharge device.

`10. The circuit of claim 7 ,in which the Control means includes meansfor producing a second control voltage varying with the rst one yand for15 2,453,711

'REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,215,197 Sherman Sept. 17, 19402,300,189 Wolff Oct. 27, 1942 2,368,449 Cook Jan. 30, 1945 Isbister eta1 Nov. 16, 1948

